1. Field of Invention
The present invention relates to a projection-type display apparatus (also called a liquid crystal projector) employing liquid crystal light valves composed of liquid crystal panels.
2. Description of Related Art
The liquid crystal projector 1100 of FIG. 9 is an example of a generally-used projection-type projector employing transmissive liquid crystal panels as light valves. In FIG. 9, light from a lamp unit 1102, serving as a light source, is reflected by a mirror 11061 and enters a light guide 1104 where the light is separated into three primary light beams, a red R light beam, a green G light beam, and a blue B light beam, by two dichroic mirrors 11081 and 11082. The blue B light beam, separated from the light by the dichroic mirror 11082, is reflected by a mirror 11062, and enters a liquid crystal light valve 1110B. The green G light beam, reflected by the dichroic mirror 11081, enters a liquid crystal light valve 1110G The red R light beam, transmitted through the dichroic mirror 11081, is reflected by two mirrors 11063, and enters a liquid crystal light valve 1110R.
The three light valves 1110R, 1110G, and 1110B are used for modulating the light beams incident thereto in accordance with their respective color image information in order to form an image. The light beams, modulated by the liquid crystal light valves 1110R, 1110G, and 1110B enter a dichroic prism 1112 from three directions. The dichroic prism 1112 consists of four right-angled prisms whose apices are brought into alignment and bonded together, with two types of wavelength selection reflecting films formed so as to form an X-shape along the bonded surfaces. Accordingly, the red R light beam is reflected by one of the two types of wavelength selection reflecting films towards a projection lens 1114. The blue B light beam is reflected by the other of the two types of wavelength selection reflecting films towards the projection lens 1114. The green G light beam transmits through the two types of wavelength selection reflecting films and arrives at the projection lens 1114. In other words, the images formed by the three liquid crystal light valves 1110R, 1110G, and 1110B, are synthesized by the dichroic prism 1112 in order to project the resultant image onto a projection surface of, for example, a screen through the projection lens 1114.
FIG. 10 is a schematic view of a liquid crystal light valve. Conventionally, as shown in FIG. 10, each of the liquid crystal light valves 1110R, 1110G, and 1110B consists of a liquid crystal panel 804, a light-incident side polarizer 803, and a light-emitting side polarizer 805, with the polarizer 803 being spaced from the light-incident surface of the liquid crystal panel 804 and the polarizer 805 being provided on the light-emitting surface of the liquid crystal panel 804.
In FIG. 10, reference numeral 803 denotes the light-incident side polarizer, which transmits, for example, a p-polarization axis component light beam 801 of the incident light (symbol  in FIG. 10 represents the p-polarization axis) and absorbs an s-polarization axis component light beam 802 (symbol ⊙ in FIG. 10 represents the s-polarization axis). The p-polarized light beams 801, transmitted through the polarizer 803, enters the liquid crystal panel 804. The liquid crystal panel 804 is a twisted nematic (TN) type liquid crystal panel, which causes the p-polarized light beam 801, incident upon a pixel to which a voltage is not applied, to leave it as an s-polarized light beam 809 by rotating the polarization axis through an angle of about 90 degrees. On the other hand, the p-polarized light beam 801, incident upon a pixel to which a voltage is applied, leaves the liquid crystal panel 804 as a p-polarized light beam 808. Reference numeral 805 denotes the light-emitting side polarizer. When the polarization axis of the polarizer 805 is set to that allowing transmission of s-polarized light beams, the light beam 809, which has left the liquid crystal panel 804 as an s-polarized light beam, transmits through the polarizer 805 unchanged. On the other hand, when the light beam 808, which has left the liquid crystal panel 804 as a p-polarized light beam, is absorbed by the polarizer 805. In the liquid crystal panel 804, the proportion of liquid crystal twisting can be controlled by controlling the voltage applied to the liquid crystal for each pixel based on each color image information, making it possible to control the amount of rotation of the polarization axis of the light beam 801, transmitted through the light-incident side polarizer 803, which enters the liquid crystal panel 804. Thus, it is possible to control the quantity of light passing through the light-emitting side polarizer 805 for every pixel in order to form an image.
The path taken by the s-polarized light beam 802 is shown at the right side in FIG. 10. The s-polarized light beam 802 is absorbed by the light-incident side polarizer 803 and is converted into heat. The light beam 808, absorbed by the light-emitting side polarizer 805, is also converted into heat.
Conventional polarizers were of the type absorbing a non-transmissive polarization axis (hereinafter referred to as an absorptive-type polarizer), so that of the randomly polarized light beams illuminating a polarizer, approximately half of it is absorbed by the polarizer, and converted into heat, deteriorating the polarization characteristics of the polarizer. In addition, when the heat produced at the polarizer is transmitted to the light crystal panel 804, liquid crystal characteristics change, or a large quantity of leakage current flows at a thin film transistor (TFT) disposed at each pixel of the liquid crystal panel, resulting in display variations.
Therefore, in conventional projection-type display apparatuses, it is necessary, for example, to use a highly heat-resistant liquid crystal, since heat is generated as a result of absorption of about half of the incident light by the light-incident side polarizer of a liquid crystal light valve. In other words, it is necessary to use a liquid crystal with a high N-I point, since physical properties, such as the refractive index, the anisotropy of dielectric constant, or the elastic constant, of the liquid crystal change with temperature, and the change becomes greater the closer the transition point (the N-I point) is to the isotropic phase. At present, a high N-I point material is mixed with ten types of materials or so, so that within, for example, the threshold voltage or response speed range providing satisfactory performance, the liquid crystal material obtained has a high N-I point at a temperature equal to or greater than 100 degrees. Thus, liquid crystals become expensive, which causes liquid crystal panels to become expensive.
In addition, in order to make the image projected onto a screen brighter, there has been a trend, in recent years, to increase the luminance of a light source lamp, resulting in the problem of increased heat generation from the liquid crystal light valves. A cooling fan for cooling the light-incident side polarizer and the liquid crystal panels is provided in order to cool the liquid crystal light valves. The designing of such a cooling fan is sophisticated since, for example, the rotational speed or the size of the cooling fan must be made large.
Further, since about half of the light from the light source lamp is absorbed by the light-incident side polarizer and converted into heat, light is used with very low efficiency, preventing a bright display from being obtained.
Accordingly, in order to overcome the above-described problems of conventional devices, it is an object of the present invention to provide a projection-type display apparatus which reduces the amount of heat generated by a liquid crystal light valve, serving as a polarizing means, and maintains excellent liquid crystal light valve characteristics. It is also an object of the present invention to provide a projection-type display apparatus which allows light from a light source lamp to be used with high efficiency.
To overcome the above-described problems, according to the present invention, there is provided a first projection-type display apparatus comprising a light source, a separating means for separating light from the light source into a plurality of color lights, a plurality of light valves for modulating each of the color lights separated by the separating means, a synthesizing means for synthesizing the color lights modulated by the plurality of light valves, and a projection optical means for projecting the light synthesized by the synthesizing means, wherein each of the light valves includes a liquid crystal panel and a polarizing means provided on the light-incident side of its associated liquid crystal panel, and wherein each of the polarizing means is formed of a multi-layered film which primarily transmits one of two types of polarization axis component light beams and primarily reflects the other of the two types of polarization axis component light beams.
In addition, according to the present invention, there is provided a second projection-type display apparatus comprising a light source, a light valve for modulating light from the light source,; and a projection optical means for projecting the light modulated by the light valve, wherein the light valve includes a liquid crystal panel and a polarizing means provided on the light-incident side of the liquid crystal panel, the polarizing means being formed of a multi-layered film which primarily transmits one of two types of polarization axis component light beams and primarily reflects the other of the two types of polarization axis component light beams, the projection-type display apparatus further comprising a polarization converter, disposed between the light source and the polarizing means, for aligning the light beams from the light source with the one type of polarization axis component light beams to emit from the polarization converter.
Further, according to the present invention, there is provided a third projection-type display apparatus comprising a light source, a light valve for modulating light from the light source, and a projection optical means for projecting the light modulated by the light valve, wherein the light valve includes a liquid crystal panel and at least a polarizing means provided on the light-emitting side of the liquid crystal panel, the polarizing means being formed of a multi-layered film which primarily transmits one of two types of polarization axis component light beams and primarily reflects the other of the two types of polarization axis component light beams, and wherein the liquid crystal panel is formed by sandwiching a liquid crystal between a pair of substrates, a switching element and a pixel electrode connected to the switching element being formed in a matrix arrangement on the inside surface of the substrate provided on the light-emitting side of the pair of substrates, and a light-shielding layer being formed on the inside surface of the substrate having formed thereon the switching element.
Still further, according to the present invention, there is provided a fourth projection-type display apparatus comprising a light source lamp, a separating means for separating light from the light source lamp into a plurality of color lights, a plurality of light valves for modulating the color lights separated from the light by the separating means, a synthesizing means for synthesizing the color lights modulated by the plurality of light valves, and a projection optical means for projecting the light synthesized by the synthesizing means, wherein each of the light valves includes a liquid crystal panel, the projection-type display apparatus further comprising a polarizing means disposed between the light source lamp and the separating means, the polarizing means being formed of a multi-layered film which primarily transmits one of two types of polarization axis component light beams and primarily reflects the other of the two types of polarization axis component light beams, a reflecting means, disposed behind the light source lamp, for reflecting the light from the light source lamp and the light reflected by the polarizing means towards the polarizing means side, and a xc2xc wavelength plate disposed between the reflecting means and the polarizing means.
Still further, according to the present invention, there is provided a fifth projection-type display apparatus comprising a separating means for separating the light from a light source into a plurality of color lights, a plurality of light valves for modulating the plurality of color lights separated from the light by the separating means, a synthesizing means for synthesizing the color lights modulated by the plurality of light valves, and a projection optical means for projecting the light synthesized by the synthesizing means, wherein the light valves include a liquid crystal panel and a polarizing means provided on the light-incident side of the liquid crystal panel associated thereto, each of the polarizing means being formed of a multi-layered film which primarily transmits one of two types of polarization axis component light beams and primarily reflects the other of the two types of polarization axis component light beams, and each of the polarizing means having a wavelength selective transmission characteristic set in such a manner as to allow selective transmission of the color lights modulated by its associated light valve.
A feature of the first through fifth projection-type display apparatuses of the present invention is that the polarizing means of each liquid crystal light valve is formed of a multi-layered film which primarily transmits one of two types of polarization axis component light beams and primarily reflects the other of the two types of polarization axis component light beams. In the present invention, such polarizing means is called either xe2x80x9creflective polarizing meansxe2x80x9d or xe2x80x9creflective polarizerxe2x80x9d. Since the amount of heat generated at such reflective polarizing means as a result of light absorption is less than that generated at conventional light absorptive-type polarizer, it is possible to prevent heat deterioration of polarizing characteristics of each polarizing means and heat influence on each liquid crystal panel. In addition, since each reflective polarizing means is a multi-layered film, it is only necessary to replace the conventional light absorptive-type polarizer with such reflective polarizing means, so that the size of the optical system is not increased. Further, the amount of heat produced is greatly reduced, so that in some cases the cooling means can be eliminated, or the cooling mechanism can be simplified, since, for example, it is no longer necessary to devise the cooling means in such a way as to increase its cooling efficiency. Still further, the polarization axis component light beams of the other type, reflected by each reflective polarizing means, are reflected at the light source, and as the beams pass through various optical members in the optical path, the polarization axis component light beams of the other type are converted into polarization axis component light beams that can transmit through each of the polarizing means. Therefore, when the reflected light beams re-enter the light-incident side polarizing means, at least part of the light reflected by the light-incident side polarizing means transmits through the liquid crystal panels to emit from them. Consequently, it is possible to use the light more efficiently than has been conventionally possible.
The multi-layered film forming its associated polarizing means of the projection-type display apparatus of the Embodiments 1 to 5 consists of alternate layers of first films and second films (described later), with the first films having a refractive index in a first axial direction of the film surface which differs from a refractive index in a second axial direction perpendicular thereto, and with the second films having a refractive index in the first axial direction and the second axial direction which is substantially equal to the refractive index of the first films in the second axial direction. This allows a flat polarizing means to be formed, so that the size of the projection-type display apparatus will not be large. In addition, in the present invention, the multi-layered film forming each of the polarizing means can be either adhered closely to or bonded to the outer surface of substrate of the associated liquid crystal panel. This makes it unnecessary to use a holding member for holding each polarizing means. It is to be noted that the polarizing means absorbs less light so that heat is not generated easily, making it unnecessary to worry about the possibility of heat affecting the liquid crystal panels.
According to the second projection-type display apparatus of the present invention, between the light source and the reflective polarizing means is provided a polarization converter which aligns a polarized light component, which becomes a reflection axis of the reflective polarizing means, with a polarization axis component which leave each of the reflective polarizing means. Therefore, most of the light from the light source transmits the each reflective light-incident side polarizing means, allowing not only even more efficient use of the light but also further reduction in the amount of heat generated at each polarizing means. The light component which could not be converted by the polarization converter can be used since the unconverted component is reflected back towards the polarization converter by each polarizing means.
According to the third projection-type display apparatus of the present invention, the above-described reflective polarizing means is used for the light-emitting side polarizing means of each liquid crystal light valve, allowing the polarization axis component of the light from each liquid crystal panel that cannot transmit through the polarizing means to be reflected back towards the light source through its associated liquid crystal panel, so that the light can be used more efficiently. When light is reflected from a light-emitting side polarizing means to its associated liquid crystal panel, a light-shielding film is provided on the light-emitting side of a switching element to prevent light from impinging upon the switching element, and, in particular, a thin-film transistor, so that even when a reflective polarizing means is used as a light-emitting side polarizing means, there is less deterioration in the liquid crystal panel characteristics. In other words, even when a reflective polarizing means is provided on the light-emitting side of a liquid crystal panel, it is possible to prevent reduced contrast caused by deterioration in the charge holding property of each pixel as a result of leakage current flowing through the silicon layer at a thin film transistor in each liquid crystal panel. Thus, deterioration in liquid crystal panel characteristics can be prevented, although using the light more efficiently.
According to the fourth projection-type display apparatus of the present invention, a xc2xc wavelength plate is disposed in front of a reflective polarizing means. The polarization axis component light beams of the other type, reflected by the polarizing means, are converted into elliptic polarized light beams by the xc2xc wavelength plate, and the elliptic polarized light beams enter and are reflected by the reflecting means at the light source lamp, and transmit through the xc2xc wavelength plate again, whereby the elliptic polarized light beams are converted into one of two types of polarization axis component light beams. Therefore, since the light can, this time, enter the polarizing means, it is possible to increase the amount of light entering the color separating means. The reflective polarizing means is disposed in front of the separating means which separates the color lights from the light source, thereby shortening the optical distance between the reflecting means and the reflective polarizing means, and fewer optical members are disposed therebetween, making it possible to achieve a smaller reduction in the amount of light as a result of repeated reflection of the light therebetween. In addition, it is desirable to dispose a second polarizing means just in front the liquid crystal panels. The polarization axis of this polarizing means is set so as to allow transmission of the light that has transmitted through the reflective polarizing means disposed in front of the separating means. As the linearly polarized light which has transmitted through the reflective polarizing means passes the color separating means, part of the linearly polarized light is converted into the other of the two types of polarization axis component, so that the polarization axis component is blocked by the second polarizing means. The second polarizing means may either be a conventional light absorptive-type polarizer or a reflecting polarizer such as those described above.
According to the fifth projection-type display apparatus of the present invention, the wavelength selective transmission characteristics of the polarizing means of each light valve are set so as to allow selective passage of the color light modulated by its associated light valve, making it possible to provide a projection-type display apparatus which has a high color reproducibility and allows a highly pure color light to enter its associated light valve. In particular, in the fifth projection-type display apparatus, the multi-layered film provided on least at the light-incident side of each liquid crystal panel consists of alternate layers of first films and second films, with the first films having a refractive index in a first axial direction of the film surface which differs from a refractive index in a second axial direction perpendicular thereto, and the second films having a refractive index in the first axial direction and the second axial direction substantially equal to the refractive index of the first films in the second axial direction. The thickness of each film is set so as to allow selective transmission of the color light incident thereupon, and the multi-layered films of the light valves may have different thickness. This allows wavelength selection at the polarizing means provided on the light-incident side of each liquid crystal panel, thereby simplifying the structure without a separate member.
In the projection-type display apparatus of the present invention, light may be made to impinge substantially perpendicular to the light-incident surface of each multi-layered film. This allows the polarization axis component light beams of the other type from the films to be reflected towards the light source along the optical axis. The light reflected at the light source can be guided again along one optical axis towards the polarizing means. Therefore, the light, reflected at the films, can be used with even greater efficiency. In detail, an optical means for collimating light beams from the light source may be disposed between the light source and the multi-layered films such that light enters substantially perpendicularly to the light-incident surface of each multi-layered film. This causes the light from the light source to enter perpendicular to the polarizing means, so that even when the polarization axis component light beams of the other type are reflected, the amount of light leakage is reduced since the light beams are reflected perpendicularly to each light-incident surface and in directions different from the optical axis direction. Accordingly, the light beams are reflected in the optical axis direction of the light source, and reflected by the light source, so that the light can be used.
In the first projection-type display apparatus, a polarization converting means which converts the light beams from the light source into polarization axis component light beams which can transmit through the polarizing means may be disposed between the light source and the separating means. This allows the randomly polarized light beams from the light source to be converted into polarization axis component light beams which transmit through the polarizing means, so that almost all of the light beams from the light source transmit through the polarizing means, as a result of which the light can be used with even greater efficiency. In addition, a smaller amount of light reflected by the polarizing means reduces the amount of light returning towards the light source, so that problems such as light leakage caused by repeated interference and reflection by the light do not occur often.
According to the first, second, fourth, and fifth projection-type display apparatuses, in the case where each light valve includes a polarizing means at the light-emitting side of its associated liquid crystal panel, each polarizing means may be a multi-layered film which primarily reflects either one of two types of polarization axis components and primarily reflects the other of the two types of polarization axis components. In that case, it is possible to reduce the amount of heat generated at each light-emitting side polarizing means, and the light, reflected by each polarizing means, transmits through each liquid crystal panel and returns back towards the light source where it is reflected for use, as a result of which the light can be used efficiently.
According to the projection-type display apparatus of each of the present inventions, in the case where light, reflected from the polarizing means, is made to return back towards the light valves by means of the light source, it is preferable that the light source be constructed so as to comprise a reflecting mirror which reflects light beams returning from the separating means as substantially collimated light beams which leave therefrom; or a reflecting mirror which reflects light beams from the separating means and a condensing means which condenses and concentrates the light beams from the reflecting mirror into substantially collimated light beams which leave therefrom.